1. Field of the Invention
The present invention is related to a novel dis-azo compound, and more particularly to a novel dis-azo compound with high molar absorption coefficient and good solubility in solvents and neutral hue.
2. Description of the Related Art
Currently, the development of flexible displays is still in research and development stage. There are a lot of developed technologies which mainly contain technologies of liquid crystal display (LCD), electrophoretic display (EPD), organic light-emitting diode (OLED), and so on. The cholesteric liquid crystal display possesses the advantages of bistable states and no need for color filters, resulting from owning color per se, but it has the disadvantages of excessively high driving voltage and slow response speed. The electrophoretic technology with high reflectivity, high contrast, and bistable states predominantly led and developed by E-ink and SiPix can be used with flexible substrates in coordination, which has currently been developed and used to manufacture commercial productions of electronic book. However, the issues for poor effect of colorization and slow response speed in the electrophoretic technology still cannot be overcome, resulting in market acceptability to be limited.
Liquavista proposed two possible display modes of color electrowetting display which belong to single-layer and multi-layer structures, respectively. The single-layer electrowetting display is manufactured by using black oil ink and color filters in coordination, whose process is simpler; however, no black oil ink with neutral hue, high oil-soluble property, high molar absorption coefficient, low viscosity, and fast response speed can be used together at the present time to enhance contrast ratio so that electrowetting technology is applied in animation.
Philips first developed a prototype of flexible display based on the electrowetting principle in September 2003, which utilizes electrowetting behavior of non-polar oil ink on hydrophobic dielectric layer as an operation principle. When no voltage is applied to elements, the affinity of non-polar oil ink to the hydrophobic dielectric layer is stronger than that of polar aqueous solution so that the oil ink is spread on the surface of hydrophobic dielectric layer, and thereby the displayed color of spread oil ink is seen when we overlook the pixels. When voltage is applied to said elements, the polar liquid is attracted by the induced charges formed on hydrophobic dielectric layer to drive the oil layer to be moved to corners of pixels, and thereby the color of the bottom of panel is seen when we overlook the pixels.
In these days, green energy-saving consciousness emerges and energy-saving and carbon reduction concepts are steadily on the increase. The electrowetting technology has evolved into the trend that can not be ignored because it can provide clear images in all lighting condition no matter when it is a sunny day or in a dim office, and merely need a tenth of power consumption of liquid crystal display with a similar size due to no need of backlight source. The energy-saving character is very suitable to be used in portable electronic product.
Reflective displays with reflectivity of more than 35% and contrast ratio of more than 15 can be manufactured by the electrowetting technology. In comparison with other display technologies, these properties are close to reflectivity of 35% and contrast of 15 of paper, so the reading comfortably of reflective displays would match with the traditional paper. Besides, one of important characters of the reflective displays is low operating voltage, resulting in not only low power consumption for driving exhibition of screen but also the ability to play continuous dynamic images.
Images displayed by changing applied voltage to control contact angle of oil ink mainly utilize the color of oil ink to display color. Therefore, the gamut of color depends on hue of oil ink. Also, dyes are the central roles for forming oil ink, so they are the core of electrowetting technology.
Elementary conditions of oil ink for electrowetting display are (1) non-polar; (2) low viscosity (<3.0 cps); (3) low surface tension (<30 mN/m); (4) requirement for ambient temperature for displays that dyes do not decompose at −10˜70° C.; (5) intensity of visible absorption uniformly covering 400-800 nm; (6) molar absorption coefficient (∈) of more than 2×103 (cm·M)−1; (7) FoM (Figure of Merit) equal to ∈×C of 100˜1000, in which C is a concentration (M); (8) hue close to standard black (L=0, a=0, b=0); (9) visible light transmittance (T %) from 10 μm test cell injected with oil ink of less than 10%.
Commercial black dyes are obtained by mixing red, yellow, and blue (i.e. three primary colors) dyes or orange, navy, and so on dyes, whose disadvantages are poor color reproducibility after mixing color due to different oil-soluble properties among dyes. Currently, no dyes with neutral hue, high oil-soluble property and excellent fastness can be provided for electrowetting technology, especially single black dye. The brightness level of each of color is mainly controlled by black. When hue is not enough neutral, deviation and distortion of color would easily occur after color combination.
Conventional dis-azo black dyes possess poor solubility in linear alkanes with long carbon chain as solvents and not enough broad and even absorption intensity of visible wavelengths at 400-800 nm. Besides, when the concentration of dye is enhanced, the viscosity would rapidly increase. Therefore, the need for light and thin electrowetting displays cannot be satisfied.
Commercial black oil ink for electrowetting display is obtained by formulating three-color (red, yellow, and blue) or two-color (red and green) oil-soluble dyes at a suitable ratio. Because the solubility of each of dyes in solvent is different, the formulated black oil ink has disadvantages of poor hue, stability, and color reproducibility; therefore, the applications of the electrowetting displays are restricted.